Separation of one liquid from a heavier liquid is commonly done by skimming or by centrifuging. A common occurrence of the use of either of these procedures is the separation of an oil contaminant from a predominant mass of water. Many coolants used in conjunction with machining operations are water-based, and become contaminated with lubricating oil. Re-use of the coolant is made more effective by the removal of the lubricating oil. This removal has the additional effect of stopping the tank of liquid from functioning as a bacterial incubator. An oil film over the water effectively excludes oxygen from the water, which would otherwise attack the bacteria. The exposure of a water film to the air on the disc (after the oil has been substantially removed) by continuing the disc rotation further improves the oxygenating process. The removal of the oil film also eliminates a class of bacteria that thrives in the oil itself, tending to produce strong odors and rancidity. The use of a partially-immersed rotating disc for removing the oil is not broadly new. These machines have had various forms of spring-loaded wiping devices securely mounted on the machine frame, and deliver the oil to a collector.